The global demand for energy and in particular liquid transport fuels continues to rise while the supply, based on ever decreasing conventional fossil reserves (e.g. oil, gas, and natural gas liquids) is threatened. A peak in oil production imposed by dwindling petroleum reserves raises the possibility of a global fuel crisis, particularly if the demand for transport fuels continues to rise as predicted. Hence, there is increased focus on the exploitation of previously unconventional fuel resources (e.g. heavy oil, oil sands, oil shale) and other non-fossil sources of energy (e.g. lignocellulosic materials).
A significant amount of research in the field of “alternative” energy production has focussed on the generation of biofuels from lignocellulosic matter. This technology raises the prospect of a shift to an abundant and renewable feedstock for energy production as an alternative to the depleting reserves of hydrocarbon-based raw materials. The enrichment of low energy density fossil fuels (e.g. lignite, peat and oil shale) into high energy fuel products also represents an attractive alternative given the relative abundance of those resources.
Despite having considerable potential most techniques for the production of fuels from lignocellulosic matter or fossilised organic materials are poorly cost-efficient and/or do not provide fuel products of adequate quality to be commercially viable. For example, current processes for the production of biofuels from lignocellulosic matter usually involve separation of feedstocks into different components via a series of complex and time-consuming steps, and in many cases require the use of expensive hydrolytic enzymes and fermenting microorganisms. In addition to these disadvantages, most current processes fail to utilise a significant proportion of feedstock material which is not converted into fuel and often goes to waste. Moreover, biofuels produced by current processes (e.g. pyrolysis) typically comprise a significantly higher oxygen content than conventional fuels. Hence, their energy density is comparatively low and their poor stability makes processing (e.g. storage, blending with conventional fuels, upgrading) difficult.
Current processes for biofuel production typically require the use of a bioreactor to generate and/or maintain the levels of heat and pressure necessary for biomass conversion. Typically, the material under treatment is maintained at target temperatures via heat transfer through reactor walls (e.g. vessel walls and/or tank walls), driven by a large temperature differential across the wall outside and inside, using heat exchangers and the like. Apart from a loss of energy, maintaining high reaction temperatures by heat transfer through reactor walls often causes hot-spots, inducing pyrolysis and carbonisation of material on the walls resulting in clogging and blockages. This is a particular issue when operating close to the pyrolysis temperature regime onset, as small fluctuations can induce significant carbonisation. Furthermore, it is difficult to achieve and maintain high target temperatures using this type of heat transfer when the diameter of the reactor is increased to accommodate treatment of large volumes of feedstock. Typically, larger vessels/tanks have reduced capacity for effective heat transfer and, hence, “scaling-up” requires the input of a much larger amount of energy coupled to an even bigger temperature differential across the wall and/or the use of an impractically large surface area to achieve high target temperatures. Transfer of heat to the material under treatment is also generally slower which can result in undesirable side reactions (e.g. polymerisations) and generally leads to lower controllability.
A need exists for improved methods and/or apparatuses for producing biofuels from organic matter which overcome at least one of the aforementioned disadvantages.